The present invention relates to a radio communication system, communication terminal apparatus, base station apparatus and a radio equalizing communication method, for use in a digital radio communication system.
Because not only sounds but also data and pictures are transmitted in multimedia movement communication, high-speed and highly reliable transmission is needed. To realize such transmission, interference between codes generated by frequency selective fading should be restrained.
As a method for restraining the frequency selective fading, there is a pre-coding technique. The pre-coding technique is a technique in which a base station performs channel estimation by the use of a received signal on a reverse link to obtain a channel estimated value and the inverse function of the obtained channel estimated value is given to a signal on a forward link and then the signal having the inverse function is transmitted to a communication terminal and thereby the necessity of the correction of the distortion of the signal on the propagation path on the communication terminal side is ideally obviated.
The pre-coding technique can presume the state of propagation paths of the forward link on the basis of a signal on the reverse link in the case where the same frequency is used for the reverse link and the forward link like the time division duplex (TDD) system, and the pre-coding technique is realized by using a tap coefficient calculated from the signal on the reverse link as it is at the time of the transmission of the signal on the forward link. Moreover, because the hardware can be concentrated on the side of the transmission unit, the technique has an advantage that the hardware configuration on the side of the reception unit can be simplified.
Hereinafter, a conventional pre-coding technique will be described by reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing the configuration of a conventional base station apparatus, and FIG. 2 is a block diagram showing the configuration of a conventional communication terminal apparatus.
The communication terminal apparatus shown in FIG. 2 performs the digital modulation of data to be transmitted in a modulation section 14 and performs the prescribed radio transmission processing of the digitally modulated data to be transmitted to transmit them to a base station apparatus through an antenna 11 as a transmission signal.
The base station apparatus shown in FIG. 1 receives the signal transmitted from the communication terminal apparatus with a plurality of antennas 1. At this time, the signal is received in the reception directivity formed by a directivity control section 2. The received signal is processed by a prescribed radio reception processing and becomes a baseband signal.
On the other hand, the channel estimation is performed by estimating the impulse response using adaptive algorithm 3. The set tap coefficient is transmitted to a replica generation section 4 and a pre-coder 9.
The replica generation section 4 obtains a candidate wave form (or a replica) by making the data pattern of the signal transmitted from the communication terminal apparatus pass through a filer on an estimated propagation path having the tap coefficient set by the adaptive algorithm 3. The replica is formed about all of the considerable data patterns.
The replica is compared with the data pattern of the signal transmitted from the communication terminal apparatus and the result of the comparison is transmitted to a judgment section 5. The judgment section 5 selects a replica being most approximate to the data pattern, and judges the data pattern corresponding to the replica to be the data pattern of the signal transmitted from the communication terminal apparatus to transmit the data pattern to an error detection section 6. The error detection section 6 performs the error detection processing of the judged data. Reception data are thereby obtained.
In the base station apparatus, data to be transmitted are transmitted to a frame formation section 8 after the data is digitally modulated in a modulation section 7. In the frame formation section 8, the data to be transmitted are configured into a frame configuration. The data configured to be the frame configuration are transmitted to a pre-coder 9.
In the pre-coder 9, the complex conjugate of the tap coefficient set by the adaptive algorithm 3 is multiplied by the data to be transmitted, and the inverse function of the impulse response on the propagation path is given to the data to be transmitted. Incidentally, at this time, divergence prevention processing such as the modulo-two operation (hereinafter referred to as MOD-2) of the transmitted data may be performed as the need arises.
The data to be transmitted to which the inverse function is given in such a way are transmitted from the antennas 1 in the directivity formed in the directivity control section 2 after a predetermined radio transmission processing of the data to be transmitted has been performed.
The signal transmitted from the base station apparatus is received by the antenna 11 of the communication terminal apparatus, and then the received signal is processed in conformity with the prescribed radio reception processing to be transmitted to a detection/de-pre-coder 12. The detection/de-pre-coder 12 demodulates the received data in conformity with the orthogonal detection or other demodulation methods. If the divergence prevention processing such as MOD-2 of the received data has been performed as mentioned above in this case, the de-pre-coder 12 presumes the received data.
The received data that has been demodulated in such a way is transmitted to an error detection section 13. The error detection section 13 performs the error detection processing to judged data.
However, in the aforesaid pre-coding technique, as shown in FIG. 3, a propagation environment is estimated on the basis of a signal received in the reception interval (RX) of the base station apparatus, and a tap coefficient obtained as the estimation result is used in the transmission interval (TX) of the base station apparatus. Consequently, because the inverse function of a channel is not updated in the reception interval of the communication terminal apparatus (corresponding to the transmission interval of the base station apparatus), there is a problem that the communication deteriorates in the reception interval of the communication terminal apparatus. The example shown in FIG. 3 is symmetrical communication, but, in case of asymmetrical communication, the pre-coding is performed by the use of a tap coefficient that has been estimated at earlier time, and the deterioration of communication becomes conspicuous. Because the rate of the asymmetrical communication becomes large in multimedia communication, this problem becomes serious.
An object of the present invention is to provide a radio communication system, communication terminal apparatus, base station apparatus and a radio communication equalizing method, capable of following the changes of a propagation environment and a capable of equalizing effectively the distortion that a signal receives in a propagation path.
The subject matter of the present invention is to decrease the load of the operation of the equalization processing in a communication terminal apparatus and to shorten the processing time of the equalization processing by using a tap coefficient set by adaptive algorithm in a base station apparatus as an initial value for omitting the processing up to initial value setting in the adaptive algorithm in the communication terminal apparatus.